1. A Comparison of the Characteristics of the Central Stars of M57 and NGC 6826 Poster – P1021 Paul Temple A Comparison of the Characteristics of the Central Stars of M57 and NGC 6826 Poster – P1021 Paul Temple Introduction: In scientific and popular literature there is a question of whether the central stars of planetary nebulae are variable. Due to the difficulties of observing these objects from ground based telescopes the answer to this question is only now being investigated. Without a space based instrument like Kepler obtaining high precision photometry, determining variability required a precision photometer or specialized CCD techniques and software. Even with these limitations progress was made. Grauer and Bond 1984 1 used a high speed photometer to discover low amplitude pulsations in Kohoutek I-16. This study led to further discovery of 16 PN and 5 pulsating PN with binary central stars Bond 2. Handler 3 points out 3 kinds of variability in central stars. Variability seems to be common in the stars studied but these studies are limited to a very small percentage of known PN due to the difficulty of observation. Introduction: In scientific and popular literature there is a question of whether the central stars of planetary nebulae are variable. Due to the difficulties of observing these objects from ground based telescopes the answer to this question is only now being investigated. Without a space based instrument like Kepler obtaining high precision photometry, determining variability required a precision photometer or specialized CCD techniques and software. Even with these limitations progress was made. Grauer and Bond 1984 1 used a high speed photometer to discover low amplitude pulsations in Kohoutek I-16. This study led to further discovery of 16 PN and 5 pulsating PN with binary central stars Bond 2. Handler 3 points out 3 kinds of variability in central stars. Variability seems to be common in the stars studied but these studies are limited to a very small percentage of known PN due to the difficulty of observation. M57and NGC 6826: In the fall of 2009 a short imaging run of 56 images was taken of PN M57with the 11” AAVSONET telescope at Astrokolkhoz Observatory 5 in Cloudcroft, NM. Each image was a 90 second exposure using an I filter. The period is ≈0.19 of a day, with a magnitude change of 0.6 magnitude. There are hints in the light curve of a possible close contact binary of a very short period, with lots of brightening and dimming that confuse the interpretation. However, the data run was of too short a duration and the image is noisy due, primarily, to the small telescope aperture. Still it showed enough promise to continue to study the stars and seek for further source of data. Kepler provided high quality data that adds to the prospect of interesting variability of central stars. Now with the Kepler data (4 runs at this time) there is enough information on NGC 6826 and M57 to compare them. NGC 6826 has a period of 0.619 of a day and a magnitude change of 10 mmag 6. These figures are much more precise than what can be obtained by an 11” ground based telescope making direct comparison difficult. The time scale of the Kepler data stretches over days while the M57 data is only over 1.5 hours. However, there is still a similar pattern to the two light curves even with the differences. In both light curves there is a close approximation to the light curve of a contact binary interspersed with chaotic light spikes of an unknown nature. Douchin et al 7 confirms the binary properties of NGC6826 in a recent paper. This opens the possibility that M57 is also a binary system with a much faster period and greater magnitude fluctuation. Without more ground and space observations the astrophysics of these objects can only be speculated. M57and NGC 6826: In the fall of 2009 a short imaging run of 56 images was taken of PN M57with the 11” AAVSONET telescope at Astrokolkhoz Observatory 5 in Cloudcroft, NM. Each image was a 90 second exposure using an I filter. The period is ≈0.19 of a day, with a magnitude change of 0.6 magnitude. There are hints in the light curve of a possible close contact binary of a very short period, with lots of brightening and dimming that confuse the interpretation. However, the data run was of too short a duration and the image is noisy due, primarily, to the small telescope aperture. Still it showed enough promise to continue to study the stars and seek for further source of data. Kepler provided high quality data that adds to the prospect of interesting variability of central stars. Now with the Kepler data (4 runs at this time) there is enough information on NGC 6826 and M57 to compare them. NGC 6826 has a period of 0.619 of a day and a magnitude change of 10 mmag 6. These figures are much more precise than what can be obtained by an 11” ground based telescope making direct comparison difficult. The time scale of the Kepler data stretches over days while the M57 data is only over 1.5 hours. However, there is still a similar pattern to the two light curves even with the differences. In both light curves there is a close approximation to the light curve of a contact binary interspersed with chaotic light spikes of an unknown nature. Douchin et al 7 confirms the binary properties of NGC6826 in a recent paper. This opens the possibility that M57 is also a binary system with a much faster period and greater magnitude fluctuation. Without more ground and space observations the astrophysics of these objects can only be speculated. Conclusion: The question of variability has been definitively answered! There is obvious variability in the central stars of some planetary nebulae. The next question is how widespread is this variability, as well as what is causing the variability. The current model of star formation and death may be challenged if it is found that a binary configuration is needed to cause the winds that define a planetary, Bond 8. With the 5 PN in the Kepler FOV it may be possible to start answering this second set of questions over the next several years. The mmag precision and long periods of coverage should provide a great deal of information and insight to sub-sequent light curves. Further ground based observations are needed to complete a picture of the physics of these most interesting stars. Careful ground based photometry of a much larger sampling of planetary nebula central stars are needed. These ground based surveys coupled with the precision of the Kepler data would at least begin to give a more complete model of the physics of the central stars of PN. Conclusion: The question of variability has been definitively answered! There is obvious variability in the central stars of some planetary nebulae. The next question is how widespread is this variability, as well as what is causing the variability. The current model of star formation and death may be challenged if it is found that a binary configuration is needed to cause the winds that define a planetary, Bond 8. With the 5 PN in the Kepler FOV it may be possible to start answering this second set of questions over the next several years. The mmag precision and long periods of coverage should provide a great deal of information and insight to sub-sequent light curves. Further ground based observations are needed to complete a picture of the physics of these most interesting stars. Careful ground based photometry of a much larger sampling of planetary nebula central stars are needed. These ground based surveys coupled with the precision of the Kepler data would at least begin to give a more complete model of the physics of the central stars of PN. References: 1 Grauer and Bond 1984, APJ 277:211-215 2 Bond and Meakes 1990 AJ, v100 # 3 3 Bond and Ciardullo 1990 ASPC 11:529B 4 Handler 1997 IAUS 180:109H 5 AAVSO Wright 28 6 Douchin and Jacoby 2011 Proceedings IAU Symposium #283 7 Douchin and Jacoby 2011 Proceedings IAU Symposium #283 8 Bond 2000 ASPC 199:115B References: 1 Grauer and Bond 1984, APJ 277:211-215 2 Bond and Meakes 1990 AJ, v100 # 3 3 Bond and Ciardullo 1990 ASPC 11:529B 4 Handler 1997 IAUS 180:109H 5 AAVSO Wright 28 6 Douchin and Jacoby 2011 Proceedings IAU Symposium #283 7 Douchin and Jacoby 2011 Proceedings IAU Symposium #283 8 Bond 2000 ASPC 199:115B Acknowledgements Thanks to Arne Henden, Executive Director of the AAVSO, Boston, MA, for giving me time on the Wright 28 telescope. His patience is appreciated. To Tom Krajci, Director of Astrokolkhoz Observatory, Cloudcroft, NM for running the AAVSONET telescopes, for his critique of the data quality and for his friendship. To my friend Rik Hill, Senior Research Scientist, Lunar and Planetary Lab, Tucson, AZ for his encouragement. Dr. Jennifer Randall, Professor of Molecular Biology, New Mexico State University, Las Cruces, NM gave great advice on the content of this poster as well as great encouragement. Also appreciation for Western New Mexico University who gives me a chance to teach astronomy and was willing to generously support this poster project! Acknowledgements Thanks to Arne Henden, Executive Director of the AAVSO, Boston, MA, for giving me time on the Wright 28 telescope. His patience is appreciated. To Tom Krajci, Director of Astrokolkhoz Observatory, Cloudcroft, NM for running the AAVSONET telescopes, for his critique of the data quality and for his friendship. To my friend Rik Hill, Senior Research Scientist, Lunar and Planetary Lab, Tucson, AZ for his encouragement. Dr. Jennifer Randall, Professor of Molecular Biology, New Mexico State University, Las Cruces, NM gave great advice on the content of this poster as well as great encouragement. Also appreciation for Western New Mexico University who gives me a chance to teach astronomy and was willing to generously support this poster project! A small portion of data from Kepler of NGC 6826. The sample was graphed by Topcat. M57 light curve from the Wright 28 11” telescope. 90 second I band images, photometry with AIP4Win and graphed by Topcat NGC 6826 Kepler data, run number one. Paul Temple, phxbird@hotmail.com, Western New Mexico University, P.O. Box 1235, Deming, NM 88031